1. Field of the Invention
The present invention relates to elastic wave devices. In particular, the present invention relates to an elastic wave device in which at least one portion of an interdigital transducer electrode is embedded in a groove located in a piezoelectric substrate.
2. Description of the Related Art
Conventionally, elastic wave devices using elastic waves such as surface acoustic waves and boundary acoustic waves have been widely used as resonators or filter devices. For example, International Publication No. WO 2006/011417 A1 proposes a surface acoustic wave device in which an interdigital transducer electrode including a laminate of a plurality of conductive films is entirely embedded in a groove formed in a piezoelectric substrate. Since the interdigital transducer electrode is entirely embedded in the groove as described in International Publication No. WO 2006/011417 A1, a surface of an insulating layer covering the interdigital transducer electrode can be planarized. As a result, the insertion loss can be reduced. International Publication No. WO 2006/011417 A1 further describes that the groove, in which the interdigital transducer electrode is embedded, has a trapezoidal shape, in lateral cross section, tapered toward the piezoelectric substrate side.
However, in the case where at least one portion of an interdigital transducer electrode is located in a tapered groove formed in a piezoelectric substrate and the interdigital transducer electrode is composed of a laminate of a plurality of conductive films, there is a problem in that it is difficult to sufficiently improve the electrical resistance of electrode fingers or characteristics, such as frequency characteristics and electric power handling capability, of an elastic wave device because an electrode formed on a sloped portion of a groove has reduced crystallinity.